<?php
/**
 * Class used internally by Text_Diff to actually compute the diffs.
 *
 * This class is implemented using native PHP code.
 *
 * The algorithm used here is mostly lifted from the perl module
 * Algorithm::Diff (version 1.06) by Ned Konz, which is available at:
 * http://www.perl.com/CPAN/authors/id/N/NE/NEDKONZ/Algorithm-Diff-1.06.zip
 *
 * More ideas are taken from: http://www.ics.uci.edu/~eppstein/161/960229.html
 *
 * Some ideas (and a bit of code) are taken from analyze.c, of GNU
 * diffutils-2.7, which can be found at:
 * ftp://gnudist.gnu.org/pub/gnu/diffutils/diffutils-2.7.tar.gz
 *
 * Some ideas (subdivision by NCHUNKS > 2, and some optimizations) are from
 * Geoffrey T. Dairiki <dairiki@dairiki.org>. The original PHP version of this
 * code was written by him, and is used/adapted with his permission.
 *
 * $Horde: framework/Text_Diff/Diff/Engine/native.php,v 1.7.2.4 2008/01/04 10:38:10 jan Exp $
 *
 * Copyright 2004-2008 The Horde Project (http://www.horde.org/)
 *
 * See the enclosed file COPYING for license information (LGPL). If you did
 * not receive this file, see http://opensource.org/licenses/lgpl-license.php.
 *
 * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
 * @package Text_Diff
 */
class Text_Diff_Engine_native {

	function diff($from_lines, $to_lines)
	{
		array_walk($from_lines, array('Text_Diff', 'trimNewlines'));
		array_walk($to_lines, array('Text_Diff', 'trimNewlines'));

		$n_from = count($from_lines);
		$n_to = count($to_lines);

		$this->xchanged = $this->ychanged = array();
		$this->xv = $this->yv = array();
		$this->xind = $this->yind = array();
		unset($this->seq);
		unset($this->in_seq);
		unset($this->lcs);

		// Skip leading common lines.
		for ($skip = 0; $skip < $n_from && $skip < $n_to; $skip++) {
			if ($from_lines[$skip] !== $to_lines[$skip]) {
				break;
			}
			$this->xchanged[$skip] = $this->ychanged[$skip] = false;
		}

		// Skip trailing common lines.
		$xi = $n_from; $yi = $n_to;
		for ($endskip = 0; --$xi > $skip && --$yi > $skip; $endskip++) {
			if ($from_lines[$xi] !== $to_lines[$yi]) {
				break;
			}
			$this->xchanged[$xi] = $this->ychanged[$yi] = false;
		}

		// Ignore lines which do not exist in both files.
		for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {
			$xhash[$from_lines[$xi]] = 1;
		}
		for ($yi = $skip; $yi < $n_to - $endskip; $yi++) {
			$line = $to_lines[$yi];
			if (($this->ychanged[$yi] = empty($xhash[$line]))) {
				continue;
			}
			$yhash[$line] = 1;
			$this->yv[] = $line;
			$this->yind[] = $yi;
		}
		for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {
			$line = $from_lines[$xi];
			if (($this->xchanged[$xi] = empty($yhash[$line]))) {
				continue;
			}
			$this->xv[] = $line;
			$this->xind[] = $xi;
		}

		// Find the LCS.
		$this->_compareseq(0, count($this->xv), 0, count($this->yv));

		// Merge edits when possible.
		$this->_shiftBoundaries($from_lines, $this->xchanged, $this->ychanged);
		$this->_shiftBoundaries($to_lines, $this->ychanged, $this->xchanged);

		// Compute the edit operations.
		$edits = array();
		$xi = $yi = 0;
		while ($xi < $n_from || $yi < $n_to) {
			assert($yi < $n_to || $this->xchanged[$xi]);
			assert($xi < $n_from || $this->ychanged[$yi]);

			// Skip matching "snake".
			$copy = array();
			while ($xi < $n_from && $yi < $n_to
			&& !$this->xchanged[$xi] && !$this->ychanged[$yi]) {
				$copy[] = $from_lines[$xi++];
				++$yi;
			}
			if ($copy) {
				$edits[] = new Text_Diff_Op_copy($copy);
			}

			// Find deletes & adds.
			$delete = array();
			while ($xi < $n_from && $this->xchanged[$xi]) {
				$delete[] = $from_lines[$xi++];
			}

			$add = array();
			while ($yi < $n_to && $this->ychanged[$yi]) {
				$add[] = $to_lines[$yi++];
			}

			if ($delete && $add) {
				$edits[] = new Text_Diff_Op_change($delete, $add);
			} elseif ($delete) {
				$edits[] = new Text_Diff_Op_delete($delete);
			} elseif ($add) {
				$edits[] = new Text_Diff_Op_add($add);
			}
		}

		return $edits;
	}

	/**
	 * Divides the Largest Common Subsequence (LCS) of the sequences (XOFF,
	 * XLIM) and (YOFF, YLIM) into NCHUNKS approximately equally sized
	 * segments.
	 *
	 * Returns (LCS, PTS).  LCS is the length of the LCS. PTS is an array of
	 * NCHUNKS+1 (X, Y) indexes giving the diving points between sub
	 * sequences.  The first sub-sequence is contained in (X0, X1), (Y0, Y1),
	 * the second in (X1, X2), (Y1, Y2) and so on.  Note that (X0, Y0) ==
	 * (XOFF, YOFF) and (X[NCHUNKS], Y[NCHUNKS]) == (XLIM, YLIM).
	 *
	 * This function assumes that the first lines of the specified portions of
	 * the two files do not match, and likewise that the last lines do not
	 * match.  The caller must trim matching lines from the beginning and end
	 * of the portions it is going to specify.
	 */
	function _diag ($xoff, $xlim, $yoff, $ylim, $nchunks)
	{
		$flip = false;

		if ($xlim - $xoff > $ylim - $yoff) {
			/* Things seems faster (I'm not sure I understand why) when the
			 * shortest sequence is in X. */
			$flip = true;
			list ($xoff, $xlim, $yoff, $ylim)
			= array($yoff, $ylim, $xoff, $xlim);
		}

		if ($flip) {
			for ($i = $ylim - 1; $i >= $yoff; $i--) {
				$ymatches[$this->xv[$i]][] = $i;
			}
		} else {
			for ($i = $ylim - 1; $i >= $yoff; $i--) {
				$ymatches[$this->yv[$i]][] = $i;
			}
		}

		$this->lcs = 0;
		$this->seq[0]= $yoff - 1;
		$this->in_seq = array();
		$ymids[0] = array();

		$numer = $xlim - $xoff + $nchunks - 1;
		$x = $xoff;
		for ($chunk = 0; $chunk < $nchunks; $chunk++) {
			if ($chunk > 0) {
				for ($i = 0; $i <= $this->lcs; $i++) {
					$ymids[$i][$chunk - 1] = $this->seq[$i];
				}
			}

			$x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $chunk) / $nchunks);
			for (; $x < $x1; $x++) {
				$line = $flip ? $this->yv[$x] : $this->xv[$x];
				if (empty($ymatches[$line])) {
					continue;
				}
				$matches = $ymatches[$line];
				reset($matches);
				while (list(, $y) = each($matches)) {
					if (empty($this->in_seq[$y])) {
						$k = $this->_lcsPos($y);
						assert($k > 0);
						$ymids[$k] = $ymids[$k - 1];
						break;
					}
				}
				while (list(, $y) = each($matches)) {
					if ($y > $this->seq[$k - 1]) {
						assert($y <= $this->seq[$k]);
						/* Optimization: this is a common case: next match is
						 * just replacing previous match. */
						$this->in_seq[$this->seq[$k]] = false;
						$this->seq[$k] = $y;
						$this->in_seq[$y] = 1;
					} elseif (empty($this->in_seq[$y])) {
						$k = $this->_lcsPos($y);
						assert($k > 0);
						$ymids[$k] = $ymids[$k - 1];
					}
				}
			}
		}

		$seps[] = $flip ? array($yoff, $xoff) : array($xoff, $yoff);
		$ymid = $ymids[$this->lcs];
		for ($n = 0; $n < $nchunks - 1; $n++) {
			$x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $n) / $nchunks);
			$y1 = $ymid[$n] + 1;
			$seps[] = $flip ? array($y1, $x1) : array($x1, $y1);
		}
		$seps[] = $flip ? array($ylim, $xlim) : array($xlim, $ylim);

		return array($this->lcs, $seps);
	}

	function _lcsPos($ypos)
	{
		$end = $this->lcs;
		if ($end == 0 || $ypos > $this->seq[$end]) {
			$this->seq[++$this->lcs] = $ypos;
			$this->in_seq[$ypos] = 1;
			return $this->lcs;
		}

		$beg = 1;
		while ($beg < $end) {
			$mid = (int)(($beg + $end) / 2);
			if ($ypos > $this->seq[$mid]) {
				$beg = $mid + 1;
			} else {
				$end = $mid;
			}
		}

		assert($ypos != $this->seq[$end]);

		$this->in_seq[$this->seq[$end]] = false;
		$this->seq[$end] = $ypos;
		$this->in_seq[$ypos] = 1;
		return $end;
	}

	/**
	 * Finds LCS of two sequences.
	 *
	 * The results are recorded in the vectors $this->{x,y}changed[], by
	 * storing a 1 in the element for each line that is an insertion or
	 * deletion (ie. is not in the LCS).
	 *
	 * The subsequence of file 0 is (XOFF, XLIM) and likewise for file 1.
	 *
	 * Note that XLIM, YLIM are exclusive bounds.  All line numbers are
	 * origin-0 and discarded lines are not counted.
	 */
	function _compareseq ($xoff, $xlim, $yoff, $ylim)
	{
		/* Slide down the bottom initial diagonal. */
		while ($xoff < $xlim && $yoff < $ylim
		&& $this->xv[$xoff] == $this->yv[$yoff]) {
			++$xoff;
			++$yoff;
		}

		/* Slide up the top initial diagonal. */
		while ($xlim > $xoff && $ylim > $yoff
		&& $this->xv[$xlim - 1] == $this->yv[$ylim - 1]) {
			--$xlim;
			--$ylim;
		}

		if ($xoff == $xlim || $yoff == $ylim) {
			$lcs = 0;
		} else {
			/* This is ad hoc but seems to work well.  $nchunks =
			 * sqrt(min($xlim - $xoff, $ylim - $yoff) / 2.5); $nchunks =
			 * max(2,min(8,(int)$nchunks)); */
			$nchunks = min(7, $xlim - $xoff, $ylim - $yoff) + 1;
			list($lcs, $seps)
			= $this->_diag($xoff, $xlim, $yoff, $ylim, $nchunks);
		}

		if ($lcs == 0) {
			/* X and Y sequences have no common subsequence: mark all
			 * changed. */
			while ($yoff < $ylim) {
				$this->ychanged[$this->yind[$yoff++]] = 1;
			}
			while ($xoff < $xlim) {
				$this->xchanged[$this->xind[$xoff++]] = 1;
			}
		} else {
			/* Use the partitions to split this problem into subproblems. */
			reset($seps);
			$pt1 = $seps[0];
			while ($pt2 = next($seps)) {
				$this->_compareseq ($pt1[0], $pt2[0], $pt1[1], $pt2[1]);
				$pt1 = $pt2;
			}
		}
	}

	/**
	 * Adjusts inserts/deletes of identical lines to join changes as much as
	 * possible.
	 *
	 * We do something when a run of changed lines include a line at one end
	 * and has an excluded, identical line at the other.  We are free to
	 * choose which identical line is included.  `compareseq' usually chooses
	 * the one at the beginning, but usually it is cleaner to consider the
	 * following identical line to be the "change".
	 *
	 * This is extracted verbatim from analyze.c (GNU diffutils-2.7).
	 */
	function _shiftBoundaries($lines, &$changed, $other_changed)
	{
		$i = 0;
		$j = 0;

		assert('count($lines) == count($changed)');
		$len = count($lines);
		$other_len = count($other_changed);

		while (1) {
			/* Scan forward to find the beginning of another run of
			 * changes. Also keep track of the corresponding point in the
			 * other file.
			 *
			 * Throughout this code, $i and $j are adjusted together so that
			 * the first $i elements of $changed and the first $j elements of
			 * $other_changed both contain the same number of zeros (unchanged
			 * lines).
			 *
			 * Furthermore, $j is always kept so that $j == $other_len or
			 * $other_changed[$j] == false. */
			while ($j < $other_len && $other_changed[$j]) {
				$j++;
			}

			while ($i < $len && ! $changed[$i]) {
				assert('$j < $other_len && ! $other_changed[$j]');
				$i++; $j++;
				while ($j < $other_len && $other_changed[$j]) {
					$j++;
				}
			}

			if ($i == $len) {
				break;
			}

			$start = $i;

			/* Find the end of this run of changes. */
			while (++$i < $len && $changed[$i]) {
				continue;
			}

			do {
				/* Record the length of this run of changes, so that we can
				 * later determine whether the run has grown. */
				$runlength = $i - $start;

				/* Move the changed region back, so long as the previous
				 * unchanged line matches the last changed one.  This merges
				 * with previous changed regions. */
				while ($start > 0 && $lines[$start - 1] == $lines[$i - 1]) {
					$changed[--$start] = 1;
					$changed[--$i] = false;
					while ($start > 0 && $changed[$start - 1]) {
						$start--;
					}
					assert('$j > 0');
					while ($other_changed[--$j]) {
						continue;
					}
					assert('$j >= 0 && !$other_changed[$j]');
				}

				/* Set CORRESPONDING to the end of the changed run, at the
				 * last point where it corresponds to a changed run in the
				 * other file. CORRESPONDING == LEN means no such point has
				 * been found. */
				$corresponding = $j < $other_len ? $i : $len;

				/* Move the changed region forward, so long as the first
				 * changed line matches the following unchanged one.  This
				 * merges with following changed regions.  Do this second, so
				 * that if there are no merges, the changed region is moved
				 * forward as far as possible. */
				while ($i < $len && $lines[$start] == $lines[$i]) {
					$changed[$start++] = false;
					$changed[$i++] = 1;
					while ($i < $len && $changed[$i]) {
						$i++;
					}

					assert('$j < $other_len && ! $other_changed[$j]');
					$j++;
					if ($j < $other_len && $other_changed[$j]) {
						$corresponding = $i;
						while ($j < $other_len && $other_changed[$j]) {
							$j++;
						}
					}
				}
			} while ($runlength != $i - $start);

			/* If possible, move the fully-merged run of changes back to a
			 * corresponding run in the other file. */
			while ($corresponding < $i) {
				$changed[--$start] = 1;
				$changed[--$i] = 0;
				assert('$j > 0');
				while ($other_changed[--$j]) {
					continue;
				}
				assert('$j >= 0 && !$other_changed[$j]');
			}
		}
	}

}
